1. Field of the Invention
The present invention relates to a manufacturing method for SiO2—TiO2 based glass used for optical members such as mirrors, photo-masks and the like in optical application technologies including a photolithographic technology. The invention also relates to a manufacturing method for a photo-mask substrate made of such glass.
2. Description of Related Art
A photolithographic process includes irradiating a photosensitive substrate with exposure light through a photo-mask. Such a photo-mask is obtained by forming a predetermined mask pattern upon a photo-mask substrate.
In recent years, the size of photosensitive substrates has increased, and, along with this, the size of photo-masks has also increased. For example, exposure devices for liquid crystal panels from the eighth generation onward use a large-sized photo-mask having a side longer than 1.2 m. A photo-mask substrate that is used for a photo-mask having such a large size can be manufactured from an SiO2 glass cylindrical ingot that is synthesized by a vapor deposition method such as the direct method, and by press-molding this ingot so as to form a flat plate-shaped member (see Japanese Laid-Open Patent Publication 2002-53330).